Our downstairs hallway light has two switches, but the one that switches it on must be used to turn it off.
From searching around, I am not sure that a previous owner hasn't added the outside light incorrectly to one of the switches.
I've drawn out the wiring to the socket and attached it. There are three cables going into a double socket. I think the issue could be with the grey and brown of the cable on the right both going to L2?
That does not look like two way wiring to me. The two switches in two way wiring are wired like for like. One should have just three wires the other of the pair 5 wires the two extra go to the light and are connected to L1 and L2.
Some times people cheat and use just two wires between the switches and borrow a line from another switch so you get a link wire. But this link goes to L1 or L2 never the Com of the two way switch.
Open the other switch of the pair. It should have 5 wires not counting the earth and if at the switch any neutral neither which is switched.
Three wires should go to one cable and these colours are like for like between the two switches. The pair of cables should go to L1 and L2 so L1 and L2 have two cables in the hole and com has a single cable in the hole.
At the switch you have sketched the link will go from either L1 or L2 on the two way switch to com on the single way switch.
There is really no way to know if L1 is always live or L2 likely easy way is trial and error. If link does not power second light when first light is off then move from L1 to L2.
[img]http://www.ericmark.talktalk.net/pictures/two-way-real.bmp[/img] Standard two way wiring J4 is the switch you say is neatly wired and that cable should go to the first switch you looked at. So at first switch you will have. COM = brown only L1 = Black plus another wire from other diagram likely black. L2 = Grey plus another wire form other diagram likely Brown. It is unknown which is permanent line but I would guess at brown first so link from brown in L2 to Com on other switch. If the second light goes off with first lamp then swap that link wire from L2 to L1.
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